The development of ultra-high-performance fiber-reinforced cement-based composites (UHP-FRCCs) was motivated by the need for a new and versatile material with high energy absorption capacity. With its excellent cracking resistance and consequent long life, UHP-FRCC is suitable for use in seismic design applications. The present study proposes a material design concept based on a multi-scale fiber-reinforcement system. In this approach, long, thick macrofibers are blended with short, thin mesofibers and microfibers. Such a combination of macrofibers, mesofibers, and microfibers is expected to enhance the mechanical properties of the composite under tension. However, the ductility of cement-based composites reinforced solely by microfibers is largely unknown. Therefore, in this study, the authors assessed whether microfiber improves the ductility of UHP-FRCC in two series of experiments. Wollastonite, which is a needle-shape mineral, is employed as a microfiber, and two different types of steel fibers are used as meso- and macrofibers. First, the enhanced toughness was evaluated in three-point bending tests on notched mortar beams. Second, the influence of wollastonite microfiber on the mechanical properties of the blended multi-scale fiber-reinforcement system was evaluated in uniaxial tension tests. Blends of macrofibers, mesofibers, and wollastonite microfibers exhibited strong reinforcement characteristics. The results indicate that the ductility of composites reinforced with wollastonite microfibers is highly dependent on the microfiber contents and type of fiber used and that blending of micro-, meso-, and macrofibers produces a highly ductile UHP-FRCC. Thus the material design concept based on the multi-scale fiber-reinforcement system proposed in this paper was shown to be effective in increasing the ductility of UHP-FRCC, even under uniaxial tension.